1. Field of the Invention
The invention generally relates to a memory disc for use in a memory disc device such as magnetic disc drives and optical disc drives, and more particularly to a memory disc having thereon a lubricant layer.
2. Description of the Prior Art
Hard disk drives (HDD) have been commonly used as auxiliary memory devices for personal computers and engineering work stations to store a large amount of information. A HDD uses a magnetic disk to read/write information on the disc. In order to deal with ever increasing information, efforts have been made to improve their capacity for a higher recording density as well as their down sizing. For example, up until 1991, the recording density on a magnetic disk was increased at the rate of about 10 times per 10 years. It was then prospected that the recording density would be 103 Mega bytes (MB)/in2 (1 Gb/in2) by the year of 2000.
However, in actuality the recording density has increased much faster than the prospect, especially in the field of 3.5 inch HDD or smaller ones, owing in part to the recent developments of a new type of magnetic heads called magnetoresistive (MR) heads and a new recording method (known as PRML method: Partial Response Maximum Likelihood method). In fact the linear recording density reached 1 Gb/in2 in 1995.
A magnetic disk, which is one of the major components of a HDD, is typically made by either one of three processes/methods: a coating method in which a resin dispersed with a mixture of aluminum and gamma iron oxide is coated on a metallic disk substrate, which is then sintered and hardened; a plating method in which a magnetic material such as CoNiP is plated on a disk substrate; and a sputter-deposition process in which gamma iron oxide is sputter-deposited to form a ferrite film on a disk substrate.
Most recent magnetic disks having intermediate sizes, i.e. 5.25 inch and smaller in diameter, are made by sputter deposition processes in forming a thin magnetic film of cobalt alloy such as CoNi, CoCrTa, and CoPtCr. This is mainly because sputter deposition processes are suited for controlling magnetic properties of a magnetic film to be deposited and for ease of realizing a higher residual magnetization density to compensate for a low linear tracking speed on a small magnetic disk.
On the other hand, efforts has been focused on an improvement of magnetic heads which facilitate an increased data storage capacity on a magnetic disc while minimizing the dimensions of the disc drive, and magnetic induction heads, which are well known magnetic heads for conventional discs, are now substituted for by a more advanced type of magnetoresistive (MR) heads. These magnetoresistive heads are highly sensitive to an externally applied magnetic field. Their sensitivity is much higher than that of conventional heads, and they are capable of providing a 5 to 10 times larger output than the conventional heads under the same operational conditions, thereby enabling a higher recording density. Recently, development of another type of sensitive magnetic heads, Giant magnetoresistive (GMR) heads having a still higher sensitivity, has been also in progress.
In this manner, magnetic disc devices have been improved intensively for a higher density and compactness, and accordingly the reduction of lift of a magnetic head (i.e. the height of the magnetic head floating over the disc) to ensure efficient read/write.
Most magnetic disc devices generally employ xe2x80x9ccontact start-stopxe2x80x9d, CSS) scheme, in which the magnetic head is at rest on a circumferential region (CSS region) of the magnetic disc within a few millimeters from the periphery of the disc during its non-operating period. As the disc is driven fast for rotation, the disc drags air with it, establishing an air flow between the magnetic head and the disc, thereby lifting or floating the head above the disc. In order to keep the magnetic head in stable equilibrium in the floating position, the head is typically provided with a head slider having a complex rail configuration to support the head. The head slider may be formed by a photo-lithography technique.
For the reduction of the lift, it is required to reduce the roughness of the disc surface so that the magnetic head will not make collision with the magnetic disc during read/write operations. However, if the roughness is too small, a net contact area between the magnetic head and the magnetic disc will become too large, which often causes the magnetic head to adhere or stick to the magnetic disc and causes it to fail to float. In fact, such adhesion can take place if the surface of the disc is lubricated by a lubricant layer having a thickness of 1.0 nm or greater. In order to avoid such adhesion, it is preferred to coat the disc with a very thin layer of lubricant, to a thickness of about a few Angstrom.
Another approach to the reduction of the possible adhesion of the magnetic head as mentioned above is a technique known as xe2x80x9cZone Texture Techniquexe2x80x9d, in which minute protrusions are provided either on the rails of a magnetic head or on the disc surface in the CSS region so as to minimize effective contact area between the magnetic head and the disc.
3. Problems to be overcome by the Invention
These protrusions, however, will result in a large pressure on the small contact area of each protrusion, and therefore it is likely that the lubricant layer in the contact area will be easily worn out if the lubricant layer is very thin. Lack of the lubricant layer in the contact area will result in solid-solid contact between the magnetic head and the disc, causing impermissible friction between them. It is often the case that protrusions are also worn out quickly under such condition.
The present inventors tried to improve wear resistance of a magnetic disc device by providing a thicker lubricant layer on the magnetic disc and forming harder protrusions on either a magnetic head or the disc. However, he has found that a thick layer of conventional lubricant on the disc cannot reduce the friction between them, due to the fact that the lubricant eventually gets moved radially outward by centrifugal forces acting on it while spinning the disc.
It is therefore an object of the invention to provide a noble magnetic disc, considering from the problems mentioned above.
It is another object of the invention to provide a noble method of manufacturing such noble magnetic disc.
It is a still another object of the invention to provide a memory disc which is less wearable.
It is a further object of the invention to provide a memory disc which may reduce wear of a head slider in a memory disc device.
In one aspect of the invention, there is provided a memory disc, comprising a lubricant layer which substantially consists only of a non-fluid bonding layer of lubricant.
In another aspect of the invention, there is provided a memory disc, comprising a lubricant layer which contains at least 90% of non-fluid bonding layer of lubricant.
In a still another aspect of the invention, there is provided a memory disc for use in a recording medium, which has an average roughness Ra of 1.0 nm or less and has a lubricant layer of 1.5 nm or greater in thickness.
In a further aspect of the invention, there is provided a memory disc drive, comprising a memory disc as mentioned above; a magnetic read/write head equipped with a head slider having slider rails which comprise on the opposite sides thereof protrusions; and a drive mechanism for driving the memory disc.
In a still further aspect of the invention, there is provided a memory disc drive, comprising a memory disc as mentioned above, a read/write head, and a drive mechanism for driving the memory disc, and protrusions on the memory disc within the CSS region thereof.
In a still further aspect of the invention, there is provided a method of manufacturing a memory disc, comprising steps of:
coating a lubricant on a disc substrate having a carbon protective layer;
providing an adhesion-treatment to the substrate so as to bond the lubricant to the disc substrate; and
removing a free fluid layer of lubricant not bonded to the disc substrate.
In the inventive method above, the lubricant may be a fluoride lubricant. The adhesion treatment may be carried out by irradiation of ultra-violet light or short-wavelength ultra-violet light, which may be done in two stages: first only on the CSS region of the disc substrate and second on the entire region of the disc substrate.
In a still further aspect of the invention, there is provided a method of manufacturing a memory disc, comprising steps of:
forming a disc substrate of an aluminum alloy;
plating the aluminum alloy disc substrate with NiP;
forming on the NiP-plated substrate an underlayer;
forming a magnetic layer on the underlayer;
forming a protective carbon film on the magnetic layer;
forming a lubricant layer on the protective carbon film, wherein the step of forming the lubricant layer further includes steps of:
coating a fluoride lubricant on the carbon protective film; and
giving an adhesion treatment to the substrate by irradiating ultra-violet light or short-wavelength ultra-violet light to the lubricant to thereby forming a non-fluid layer (bonding layer) of lubricant; and
removing free fluid layer of lubricant from the substrate.
A typical example of memory discs is a magnetic disc or an optical disc.
It should be noted that as mentioned above the invention utilizes a non-fluid bonding layer as a lubricant layer on the memory disc for facilitating reduction of the friction between the head slider of a head and the memory disc during read/write operations by the head while it is in rotational motion over the disc, thereby reducing the wear of the lubricant layer caused by the friction.
With a thicker lubricant layer in the CSS region than in the data region, friction between the lubricant layer and the head slider is greatly reduced in the CGS region, so that the lubricant layer will become durable over extended periods of time.
Embodiments of memory disc, manufacturing method thereof, and method of manufacturing disc drive utilizing such memory disc in accordance with the present invention will be explained in detail with reference to the accompanying drawings hereinafter.